STUDY DESIGN: Prospective study with patient and physician questionnaires, clinical records, and imaging. OBJECTIVE: To compare physician expectations of surgery for sciatica and patient outcome. SUMMARY OF BACKGROUND DATA: Physician accuracy in identifying individual patient prognosis is important for therapeutic decisions. METHODS: A total of 197 consecutive patients with low back pain and/or sciatica who underwent low back surgery in the University Hospital of Lausanne, Switzerland. RESULTS: Physicians predicted "a great improvement" of quality of life after surgery for 79% and "moderate improvement" for 20% (1% others); 39% of patients had no "minimal clinically important difference" in back pain after surgery, despite physician prediction of "great improvement." Correlations between physician expectation and various dimensions of patient outcome were not significant, and agreement with patient global judgment of 1-year outcome was poor (kappa = 0.03). However, in a subgroup where the indication for treatment was not considered appropriate, physician prediction of "great improvement" was followed by greater improvement outcome on SF-36 mental component score (P = 0.05), mental health (0.02), and general health (0.03) compared with patients where the physician did not predict "great improvement." CONCLUSION: Despite clear average improvement, surgeons tended to give overly optimistic predictions that were not correlated with patient outcome. For patients receiving a treatment not meeting explicit criteria of appropriateness, more optimistic physician expectation was associated with better improvement of psychological dimensions. Besides prognostic ability, the influence of physician expectation on patient outcome is discussed and the concept of "curabo effect" (differentiated from "placebo effect") proposed.